The present invention generally relates to making a microstructure by surface micromachining. One aspect relates to making a structurally reinforced microstructure to provide a flatter profile on one or more of its structural layers. Another aspect relates to providing a plurality of at least generally laterally extending etch release channels to facilitate the release of the microstructure from the substrate.
There are a number of microfabrication technologies that have been utilized for making microstructures (e.g., micromechanical devices, microelectromechanical devices) by what may be characterized as micromachining, including LIGA (Lithographie, Galvonoformung, Abformung), SLIGA (sacrificial LIGA), bulk micromachining, surface micromachining, micro electrodischarge machining (EDM), laser micromachining, 3-D stereolithography, and other techniques. Bulk micromachining has been utilized for making relatively simple micromechanical structures. Bulk micromachining generally entails cutting or machining a bulk substrate using an appropriate etchant (e.g., using liquid crystal-plane selective etchants; using deep reactive ion etching techniques). Another micromachining technique that allows for the formation of significantly more complex microstructures is surface micromachining. Surface micromachining generally entails depositing alternate layers of structural material and sacrificial material using an appropriate substrate which functions as the foundation for the resulting microstructure. Various patterning operations may be executed on one or more of these layers before the next layer is deposited so as to define the desired microstructure. After the microstructure has been defined in this general manner, the various sacrificial layers are removed by exposing the microstructure and the various sacrificial layers to one or more etchants. This is commonly called xe2x80x9creleasingxe2x80x9d the microstructure from the substrate, typically to allow at least some degree of relative movement between the microstructure and the substrate. Although the etchant may be biased to the sacrificial material, it may have some effect on the structural material over time as well. Therefore, it is generally desirable to reduce the time required to release the microstructure to reduce the potential for damage to its structure.
Microstructures are getting a significant amount of attention in the field of optical switches. Microstructure-based optical switches include one or more mirror microstructures. Access to the sacrificial material that underlies the support layer that defines a given mirror microstructure is commonly realized by forming a plurality of small etch release holes down through the entire thickness or vertical extent of the mirror microstructure (e.g., vertically extending/disposed etch release holes). The presence of these small holes on the upper surface of the mirror microstructure has an obvious detrimental effect on its optical performance capabilities. Another factor that may have an effect on the optical performance capabilities of such a mirror microstructure is its overall flatness, which may be related to the rigidity of the mirror microstructure. xe2x80x9cFlatnessxe2x80x9d may be defined in relation to a radius of curvature of an upper surface of the mirror microstructure. This upper surface may be generally convex or generally concave. Known surface micromachined mirror microstructures have a radius of curvature of no more than about 0.65 meters.
The present invention is generally embodied in a method for making a microstructure by surface micromachining. In this method, at least one and more typically a plurality of at least generally laterally extending etch release channels or conduits are formed within a sacrificial material. This sacrificial material is used to fabricate the microstructure on an appropriate substrate. At least some of this sacrificial material is removed when the microstructure is released from the substrate (and thereby encompassing the situation where all of this sacrificial material is removed).
A first aspect of the present invention is embodied in a method for making a microstructure by surface micromachining that includes forming a first structural layer over a sacrificial material. xe2x80x9cOverxe2x80x9d includes being deposited directly on the substrate or being deposited on an intermediate layer that is disposed between the subject sacrificial layer and the substrate. xe2x80x9cOnxe2x80x9d in contrast means that there is an interfacing relation. In any case, a plurality of hollow etch release pipes, channels, conduits, or the like extend at least generally laterally through/within this sacrificial material. Lateral or the like, as used herein, means that the etch release conduits are disposed or oriented in a direction which is at least generally parallel with the substrate. Although the etch release conduits will typically extend laterally at a constant elevation relative to the substrate, such need not necessarily be the case. Ultimately, at least some of the sacrificial material is removed at least in part by allowing an etchant to flow through any and all of these hollow etch release conduits (and thereby encompassing the situation where all of this sacrificial layer is removed).
Various refinements exist of the features noted in relation to the first aspect of the present invention. Further features may also be incorporated in the first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. In one embodiment, at least one end of at least one etch release conduit may be disposed at least generally at the same radial position as a perimeter of the first structural layer. Hereafter, xe2x80x9cat least generally at the same radial positionxe2x80x9d in relation to any end of any etch release conduit or structure used to define the same means within 50 xcexcm of the radial position of the perimeter of the relevant structural layer in one embodiment, more preferably within 25 xcexcm of the radial position of the perimeter of the relevant structural layer in another embodiment, and even more preferably at the same radial position as the perimeter of the relevant structural layer. As such, the etchant does not have to etch in from the perimeter xe2x80x9ctoo farxe2x80x9d before encountering an open end of one or more etch release conduits associated with the first aspect. Reducing the time required for the etchant to reach the etch release conduits should at least to a point reduce the overall time for accomplishing the release of the microstructure from the substrate.
Various layouts of the plurality of etch release conduits in the noted lateral dimension may be utilized in relation to the first aspect. In one embodiment, each of the plurality of etch release conduits may be disposed in non-intersecting relation, in another embodiment the plurality of etch release conduits are disposed in at least substantially parallel relation, and in yet another embodiment at least some of the etch release conduits intersect. The plurality of etch release conduits may extend at least generally toward (and thereby including to) a common point, such as one that corresponds with a center of the first structural layer in the lateral dimension. All etch release conduits need not extend the same distance toward this common point, although such may be the case. Some of the plurality of etch release conduits may extend at least generally toward (and thereby including to) a first common point (e.g., one that corresponds with a center of the first structural layer in the lateral dimension), while some of the plurality of etch release conduits may extend toward a different common point. The plurality of etch release conduits may also extend in the lateral dimension in a variety of configurations. In one embodiment, the plurality of etch release conduits are at least generally axially extending, while in another embodiment the plurality of etch release conduits are non-linear (e.g., in a sinusoidal configuration that is at least generally parallel with the substrate).
In one embodiment of the first aspect, the laterally extending etch release conduits are completely defined before the stack that includes the microstructure being fabricated by the methodology of the first aspect is exposed to a release etchant for removing the first sacrificial layer. One particularly desirable application for the first aspect is in the formation of a mirror microstructure or multiple mirror microstructures for a surface micromachined optical system that has at least some degree of movement relative to the first substrate. Because of the presence of the plurality of laterally extending etch release conduits, there is no need to have a plurality of etch release apertures or holes that extend entirely down through the entire vertical extent of the first structural layer to remove the sacrificial material that directly underlies this first structural layer. That is, there is no need for a plurality of vertically disposed etch release apertures, with xe2x80x9cverticalxe2x80x9d being at least generally opposite xe2x80x9clateral.xe2x80x9d As such, the upper surface of the first structural layer retains a very smooth surface that lacks any such vertically disposed etch release apertures, which makes the microstructure that is made by the methodology of the first aspect particularly suited for use in optical applications. This is true whether the upper surface of the first structural layer is the actual optical surface for the mirror microstructure, or whether a film or other layer is deposited on the first structural layer to provide more desirable optical properties/characteristics.
The sacrificial material that directly underlies the first structural layer used by the first aspect may actually be defined by the sequential deposition of multiple sacrificial layers, one on top of the other. That is, a lower portion of this sacrificial material may be formed as one layer, and an upper portion of this sacrificial material may be subsequently formed in overlying relation. Consider a case where a first sacrificial layer is formed over the first substrate, and where a first intermediate layer is formed on this first sacrificial layer. The first intermediate layer may be patterned to define a first subassembly (e.g., a plurality of strips). Portions of the first sacrificial layer are exposed by a patterning of the first intermediate layer to define the first subassembly. An upper portion of the first sacrificial layer (i.e., something less than the entirety of the first sacrificial layer) may be etched an amount after this patterning such that at least part of the first sacrificial layer that underlies at least part of the first subassembly is removed (e.g., using a timed etch). The first subassembly may be disposed directly on the first sacrificial layer, directly on a structural layer, or directly on both the first sacrificial layer and a structural layer (e.g., for the case where there is both a sacrificial material and a structural material at the same level within a stack which contains the microstructure being fabricated by the methodology of the subject first aspect).
The xe2x80x9cgapxe2x80x9d that now exists between the first subassembly and that portion of the etched first sacrificial layer that is directly beneath the first subassembly may be characterized as an undercut. A second sacrificial layer may be formed on at least the first sacrificial layer. One could characterize this as xe2x80x9cbackfilling.xe2x80x9d Notwithstanding this characterization of the backfilled sacrificial material as a xe2x80x9csecond sacrificial layerxe2x80x9d, the first and second sacrificial layers may in fact be indistinguishable from each other and may in effect define a continuous structure. Nonetheless, the sacrificial material that has been characterized as the second sacrificial layer will not fill the entire extent of each of the undercuts. This failure to fill the undercuts defines the plurality of etch release conduits that are associated with the first aspect of the present invention. One could visualize that the first subassembly acts as an umbrella of sorts that prevents the material that has been characterized as the second sacrificial layer from totally filling the noted undercuts that are protected by the first subassembly. Typically the second sacrificial layer will also cover the first subassembly. In this case and possibly in other instances during the fabrication of the microstructure associated with the first aspect, it may be desirable to planarize an upper surface of a given layer before depositing the next layer thereon. One appropriate technique for providing this planarization function is chemical mechanical polishing.
The first subassembly may be a reinforcing structure for the first structural layer, in which case the first subassembly would exist in the microstructure that is defined by the methodology of the first aspect. Reinforcement may be provided by structurally interconnecting the first structural layer with the first subassembly through the above-noted second sacrificial layer which may be deposited on the first subassembly in addition to the first sacrificial layer as noted. Further reinforcement of the first structural layer may be accomplished by structurally interconnecting the first subassembly with a structural layer that underlies the first sacrificial layer. In both cases, the actual reinforcement structure could be in the form of a plurality of posts or columns that are disposed in spaced relation, in the form of a plurality of at least generally laterally extending ribs or rails, or in the form of a grid-like reinforcement structure.
The first subassembly need not remain in the microstructure that may be defined by the methodology of the first aspect. That is, the first subassembly need not be part of the final microstructure that is ultimately fabricated by the methodology of the first aspect. In this case, the only purpose of the first subassembly would be to at least assist in the formation of the plurality of etch release conduits that are associated with the first aspect of the present invention. This xe2x80x9ctemporaryxe2x80x9d first subassembly may be in the form of a plurality of rails that are formed on or in a sacrificial material that is used in the methodology of the first aspect. Removal of the first subassembly from the final microstructure being made by the subject first aspect may be desirable in order to retain a low mass for this microstructure (e.g., in an upper structural layer of such a microstructure).
One way in which the first subassembly may be removed or alleviated from the final microstructure being made by the first aspect of the present invention is to form the first subassembly from a material that would be etched away along with the various sacrificial layers, although possibly at a different rate. Appropriate materials for the first subassembly in this case include silicon nitride, poly-silicon-germanium, or any other material that is soluble in the release etch or other etchant that will not have an adverse effect on any of the structural layers that may be included in the microstructure being made by the methodology of the subject first aspect. Having the first subassembly be of a reduced thickness may also contribute to the first subassembly being removed along with the sacrificial material within a desired time when releasing the microstructure made by the methodology of the first aspect. In one embodiment where the first subassembly is formed from silicon nitride and in the form of a plurality of strips, the first subassembly has a thickness or vertical extent of typically less than about 1,500 xc3x85 for this purpose.
Another option for creating the plurality of at least generally laterally extending etch release channels in accordance with the first aspect entails forming a first intermediate layer that will underlie the first sacrificial layer. This first intermediate layer may be patterned to define a plurality of at least generally laterally extending strips that are disposed in non-intersecting relation over at least a portion of their length. These strips are spaced relatively close to each other such that when the first sacrificial layer is deposited on the first intermediate layer, the sacrificial material is unable to entirely fill the space between the adjacent strips. More specifically, an upper portion of the space between adjacent strips will xe2x80x9cclose offxe2x80x9d during the deposition of the material that defines the first sacrificial layer before a lower portion of the space between the adjacent strips has had a chance to be filled with the material that defines the first sacrificial layer. Each xe2x80x9cunfilledxe2x80x9d void between adjacent pairs of strips defines one of the plurality of etch release channels referenced in relation to the first aspect. The manner in which the voids are formed may be characterized as xe2x80x9ckeyholing.xe2x80x9d Keyholing in relation to the first aspect is a result a relatively close spacing between adjacent strips in relation to their thickness or vertical extent. In one embodiment, a ratio of the height of these strips to the spacing between adjacent strips is at least about 1:1.
Further options exist for creating the plurality of at least generally laterally extending etch release channels in accordance with the first aspect. One way is to use multiple, different etchants. A first etchant that is not selective to the first sacrificial layer may be used to form the plurality of at least generally laterally extending etch release channels. A second, different etchant that is selective to the first sacrificial layer may thereafter be directed through the plurality of at least generally laterally extending etch release channels or conduits (again created/defined by the first etchant) to remove the first sacrificial layer. The first etchant may be selective to a material that forms a plurality of at least generally laterally extending etch release rails that are embedded or encased within the first sacrificial layer or at least in a sacrificial material. Any appropriate layout may be utilized for these plurality of at least generally laterally extending etch release rails, including a plurality of separate and discrete etch release rails, a network or grid of interconnected etch release rails, or some combination thereof.
The intermediate structure in the fabrication of the microstructure in accordance with the first aspect may be characterized as a stack, and includes the various layers that are sequentially deposited on the substrate, and thereafter possibly patterned. This stack includes an exterior surface that is opposite the first substrate. Access to at least one of the etch release rails in the above-noted two etchant example may be provided by a first runner that extends from this exterior surface of the stack and at least generally toward the first substrate to a level such that it may structurally interconnect with at least one of the plurality of etch release rails. The same material that defines the etch release rails may define this first runner, such that the first etchant will first remove the first runner, and then each etch release rail that is structurally interconnected therewith (either directly or indirectly). Multiple first runners may be provided for accessing the plurality of etch release rails, multiple etch release rails may be accessed by a single first runner, or some combination thereof.
A second aspect of the present invention is embodied in a method for making a microstructure in which a plurality of at least generally laterally extending etch release channels or conduits are formed within a sacrificial material that is used to build/assemble the microstructure on an appropriate substrate, but which is at least in part removed when the microstructure is released from this substrate. These etch release channels do not exist until the release of the microstructure is initiated in the second aspect. In this regard, the method of the second aspect includes forming a first intermediate layer on top of a first sacrificial layer or possibly on top of the substrate. This first intermediate layer is patterned to define a plurality of at least generally laterally extending first strips that sit on top of the first sacrificial layer. A second sacrificial layer is thereafter deposited on that portion of the first sacrificial layer which was exposed by the patterning of the first intermediate layer so as to be disposed at least alongside the first strips. Although not fundamentally required by the second aspect, the second sacrificial layer may also be disposed on top of the first strips as well. In any case, a first structural layer is formed on top of the second sacrificial layer. Both the first and second sacrificial layers are removed at least in part using an appropriate etchant. Generally, those portions of the second sacrificial layer that interface with or are disposed adjacent to the first strips etch at a greater rate than other portions of the second sacrificial layer which effectively defines a plurality of at least generally laterally extending etch release pipes, channels, conduits or the like. A plurality of hollow and at least generally laterally extending etch release channels or conduits (e.g., disposed at least generally parallel with an upper surface of the first substrate) are thereby formed in the second sacrificial layer by this differential etch rate. Although these etch release conduits will typically be disposed at a constant elevation relative to the substrate, such need not necessarily be the case. Ultimately, at least part of the second sacrificial layer, as well as the first sacrificial layer, are removed at least in part by allowing an etchant to flow through any and all of the noted conduits after the formation of the same in the releasing operation (and thereby encompassing the situation where all of the first and second sacrificial layers are removed, as well as the first intermediate layer if the same is not a structural material as discussed below).
Various refinements exist of the features noted in relation to the second aspect of the present invention. Further features may also be incorporated in the second aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The noted differential etch rate is believed to be based upon the density of that portion of the second sacrificial layer in proximity to the first strips being less than a density of the remainder of the second sacrificial layer, as well as a density of the first sacrificial layer as well for that matter. The differential density is due to the sticking characteristics of the depositing atoms or molecules, which depends on the characteristics of the deposition technique. For example, the density of add-on molecules in a plasma-enhanced chemical vapor deposition (PECVD) system depends on directional orientation of the surface to the plasma body. In this way, atoms or molecules striking the surface have different energy available to them to aid in their positioning in low-energy (i.e. high-density) positions on the surface.
In one embodiment of the second aspect, at least one end of at least one first strip may be disposed at least generally at the same radial position as a perimeter of the first structural layer. Since the first strips effectively define the etch release conduits, at least one end of at least one etch release conduit may be disposed at this same radial position as well. As such, the etchant does not have to etch in from the perimeter xe2x80x9ctoo farxe2x80x9d before encountering a region that will have a higher etch rate, and that again defines a corresponding etch release conduit. The parameters mentioned above in relation to the first aspect regarding this feature are equally applicable to this second aspect.
Various layouts of the plurality of first strips (and thereby the etch release conduits) in the noted lateral dimension may be utilized in accordance with the second aspect. In one embodiment, each of the plurality of at least generally laterally first strips are further disposed in non-intersecting relation, in another embodiment each of the plurality of first strips are disposed in at least substantially parallel relation, and in yet another embodiment at least some of the first strips intersect. The plurality of first strips may extend at least generally toward (and thereby including to) a common point, such as one that corresponds with a center of the first structural layer in the lateral dimension. All of the first strips need not extend the same distance toward this common point, although such may be the case. Some of the plurality of strips may extend at least generally toward (and thereby including to) a first common point (e.g., one that corresponds with a center of the first structural layer in the lateral dimension), while some of the plurality of first strips may extend toward a different common point. The plurality of first strips utilized by the second aspect may also extend in the lateral dimension in a variety of configurations. In one embodiment, the plurality of first strips are at least generally axially extending, while in another embodiment the plurality of first strips are non-linear (e.g., in a sinusoidal configuration within a plane that is parallel with the substrate).
One particularly desirable application for the second aspect is in the formation of a mirror microstructure or multiple mirror microstructures for a surface micromachined optical system that has at least some degree of movement relative to the first substrate. Because of the different etch rates that result from the way in which the microstructure is made by the methodology of the second aspect, there is no need to have a plurality of vertically disposed etch release apertures that extend down entirely through the second structural layer to release the mirror microstructure from the first substrate by the removal of the underlying first and second sacrificial layers. As such, the upper surface of the second structural layer retains a very smooth surface that lacks any such vertically disposed etch release apertures, which makes the microstructure that is made by the methodology of the second aspect particularly suited for use in optical applications. This is true whether the upper surface of the second structural layer is the actual optical surface for the mirror microstructure, or whether a film or other layer is deposited on the second structural layer to provide more desirable optical properties/characteristics.
Typically the second sacrificial layer will also cover the first strips (again, formed from the first intermediate layer) such that they are effectively embedded between the first and second sacrificial layers. In this case, it may be desirable to planarize an upper surface of the second sacrificial layer before depositing the first structural layer thereon. It may also be desirable to planarize an upper surface of other layers within the microstructure made in accordance with the methodology of the second aspect as well before depositing another layer thereon. One appropriate technique for executing this planarization function is chemical mechanical polishing.
The first strips may be a reinforcing structure for the first structural layer and would then exist in the microstructure that is made by the methodology of the second aspect. Reinforcement may be provided by structurally interconnecting the first structural layer with the first strips through the above-noted second sacrificial layer which may be deposited on the first strips in addition to the first sacrificial layer as noted. Further reinforcement of the first structural layer may be accomplished by structurally interconnecting the first strips with a structural layer that underlies the first sacrificial layer and thereby the first structural layer. In both cases, the actual reinforcing structure could be in the form of a plurality of posts or columns that are disposed in spaced relation, in the form of a plurality of at least generally laterally extending ribs or rails, or in the form of a grid-like reinforcement structure.
A third aspect of the present invention is embodied in a method for making a surface micromachined microstructure. A first sacrificial layer is formed over a first substrate in a manner so as to define a plurality of at least generally laterally extending low density regions therein. A first structural layer is thereafter formed over the first sacrificial layer. The release of the first structural layer from the first substrate is affected by removing the first sacrificial layer with an appropriate etchant. The etching rate within the low density regions of the first sacrificial layer is greater than in other regions of the first sacrificial layer.
Various refinements exist of the features noted in relation to the third aspect of the present invention. Further features may also be incorporated in the third aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The higher etch rate in the low density regions of the first sacrificial layer may define a plurality of at least generally laterally extending etch release pipes, channels, conduits, or the like, which in turn should reduce the time required to completely release the microstructure from the first substrate. Although the low density regions will typically be disposed at a constant elevation relative to the substrate, such need not be the case.
In one embodiment of the third aspect, at least one end of at least one low density region may be disposed at least generally at the same radial position as a perimeter of the first structural layer. Since the low density regions effectively define the etch release conduits, at least one end of at least one etch release conduit may be disposed at this same radial position as well. As such, the etchant does not have to etch in from the perimeter xe2x80x9ctoo farxe2x80x9d before encountering a low density region for definition of an etch release conduit(s). The parameters mentioned above in relation to the first aspect regarding this feature are equally applicable to this third aspect.
Various layouts of the plurality of low density regions, and thereby the etch release conduits, in the noted lateral dimension may be utilized in accordance with the third aspect. In one embodiment, each of the plurality of at least generally laterally extending low density regions are disposed in non-intersecting relation, in another embodiment each of the plurality of low density regions are disposed in at least substantially parallel relation, and in yet another embodiment at least some of the low density regions intersect. The plurality of low density regions may extend at least generally toward (and thereby including to) a common point, such as one that corresponds with a center of the first structural layer in the lateral dimension. All of the low density regions need not extend the same distance toward this common point, although such may be the case. Some of the plurality of low density regions may extend at least generally toward (and thereby including to) a first common point (e.g., one that corresponds with a center of the first structural layer in the lateral dimension), while some of the plurality of low density regions may extend toward a different common point. The plurality of low density regions utilized by the third aspect may also extend in the lateral dimension in a variety of configurations. In one embodiment, the plurality of low density regions are at least generally axially extending, while in another embodiment the plurality of low density regions are nonlinear (e.g., in a sinusoidal configuration within a plane that is at least generally parallel with the substrate).
One way in which the low density regions associated with the third aspect may be formed is by forming a second sacrificial layer over the first substrate, and then patterning the same to define a plurality of at least generally laterally extending etch release conduit apertures. Each of these etch release conduit apertures is defined by first and second sidewalls that are disposed in spaced relation to each other. The first sacrificial layer is formed such that the material of the first sacrificial layer is deposited within these etch release conduit apertures. The first sacrificial layer may be deposited on the top of the second sacrificial layer as well. In any case, the low density regions associated with the third aspect will thereby exist along the first and second sidewalls of each of the etch release conduit apertures.
One advantage of the above-noted method for defining the low density regions in accordance with the third aspect, and thereby for defining a plurality of etch release channels, is that a layout of the low density regions may define a network or grid-like structure or such that a plurality of these low density regions cross and/or are interconnected in some manner. For instance, the patterning of the second sacrificial layer could define a repeating pattern of interconnected xe2x80x9cdiamonds,xe2x80x9d a honeycomb or honeycomb-like structure, or the like. This ability to define a network could further enhance the distribution of the etchant during the release of the first structural layer from the first substrate. Another advantage of this particular method for defining the low density regions, and thereby for defining a plurality of etch release channels, is that the same does not require the use of any structural layer or material for the formation thereof. Therefore, this particular embodiment of the third aspect could be used to enhance the release of a simple, single structural layer in a microstructure.
The above-noted methodology for defining the low density regions in accordance with the third aspect may also be utilized where structural reinforcement of the first structural layer is desired. Structural reinforcement of the first structural layer may be realized by having an appropriate reinforcement structure cantilever downwardly from a lower surface of the first structural layer. Another way to structurally reinforce the first structural layer is to structurally interconnect the first structural layer with an underlying structural layer. The only limitation on the use of any such reinforcement structure is that it should not extend downwardly through any of the noted low density regions so as to cut off any etch release channels. This may be done in variety of manners. Consider the case where the second sacrificial layer is patterned in the form of a honeycomb. A plurality of columns or posts could extend downwardly from the first structural layer through the xe2x80x9cclosed cellxe2x80x9d portions of the honeycomb without intersecting with any of the low density regions which define the profile of the honeycomb (in plan view).
Notwithstanding the advantages of the above-noted method for forming the low density regions in accordance with the third aspect, these low density regions may also be defined in the manner discussed above in relation to the second aspect. Therefore, those features discussed above in relation to the second aspect may be used in this third aspect as well.
A fourth aspect of the present invention is embodied in a method for making a surface micromachined microstructure. A first sacrificial layer is formed over a first substrate. A first structural layer is formed over the first sacrificial layer. The release of the first structural layer from the first substrate is affected by what may be characterized as a two step etch. In this regard, a first etchant may be used to form a plurality of at least generally laterally extending etch release channels or conduits within the first sacrificial layer or so as to otherwise be embedded within a sacrificial material. A second, different etchant that is selective to the first sacrificial layer may thereafter be directed through the plurality of at least generally laterally extending etch release channels (again created/defined by the first etchant) to remove the first sacrificial layer.
Various refinements exist of the features noted in relation to the fourth aspect of the present invention. Further features may also be incorporated in the fourth aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The first etchant may be selective to a material that forms a plurality of at least generally laterally extending etch release rails that are embedded or encased within the first sacrificial layer or at least in a sacrificial material. Any appropriate layout may be utilized for these plurality of at least generally laterally extending etch release rails, including a plurality of separate and discrete etch release rails, a network or grid of interconnected etch release rails, or some combination thereof.
The intermediate structure in the fabrication of the microstructure in accordance with the fourth aspect may be characterized as a stack, and includes the various layers that are sequentially deposited on the substrate, and thereafter possibly patterned. This stack includes an exterior surface that is opposite the first substrate. Access to at least one of the noted etch release rails may be provided by a first runner that extends from this exterior surface of the stack and at least generally toward the substrate to a level such that it may interconnect with at least one of the plurality of etch release rails. The same material that defines the etch release rails may define this first runner, such that the first etchant will first remove the first runner, and then each etch release rail interconnected therewith. Multiple first runners may be provided for accessing the plurality of etch release rails, multiple etch release rails may be accessed by a single first runner, or some combination thereof.